Paving stones of differing shapes have been employed in the construction of traffic-carrying surfaces such as roadways, footways, embankments and pool decks. Typically, the paving stones are made of concrete, formed in desired shape in molds, and cured under high pressure where the paving stone material is compacted and hardened into the desired shape in the mold, and removed from the mold and exposed to ambient air to complete the curing cycle. The method by which such paving stones can be made are well known in the art and form no part of my invention. Hence, methods for making paving stones will not be addressed further except to note that the shape of the molds used to form prior art paving stones must be modified so as to conform to the shape of my paving stones. To construct a surface employing paving stones, the undersurface is prepared in known fashion to provide a smooth flat surface upon which to place the paving stones. The paving stones are placed one at a time such that their vertical or peripheral walls or edge faces come into close contact. The gaps between edge faces may be filled either with mortar, concrete, or other such solidifying spacer element, or preferably, with sand which is simply poured into the gaps in a known manner. My invention is ideally suited to the latter, less costly method. The traffic load encountered by surfaces constructed in the above manner can vary from as light as pedestrian traffic to as heavy as several ton trucks and forklifts.
Paving stones employed for traffic surfaces have come in a wide variety of shapes from square and rectangular to multi-sided and irregular shaped surfaces, but a paving stone's shape is known to affect the ground cover's load carrying capacity and durability. When viewed from the top, such paving stones generally fall into one of three basic categories.
The first category is a paving stone which has a known and simple geometric shape, such as a rectangle, a square, a hexagon, or an octagon. This category is less desirable than other categories hereinafter discussed because their shapes preclude an interlock joint between adjacent paving stones. Additionally, proper utilization can require greater material and care than other paving stones and are often not satisfactory in use. For example, if such paving stones were placed in the manner expected of my invention, i.e., with sand between them, the surface would not be stable because there is no interlock. Furthermore, because there is no interlock, long, straight channels are more easily formed between the paving stones thus permitting rain, for example, to wash away the sand further reducing the load carrying stability of the ground cover formed with those paving stones. Hence, such paving stones would typically require mortar or concrete between paving stones. Mortar or concrete are typically more expensive than sand and are more difficult to work with.
A second category of paving stone is one wherein, from a top plan view, the paving stone looks substantially rectangular but the edges are deformed in such a manner as to interlock when laid next to an adjacent, identical stone. Examples of second category paving stones are shown in U.S. Pat. No. 2,919,634 and U.S. Pat. No. 3,494,266. Also included in this category are certain multi-faced irregularly shaped paving stones such as that disclosed in U.S. Pat. No. Des. 82,970. The paving stones disclosed in the aforementioned patents overcome some of the drawbacks of paving stones discussed in the preceding paragraph because they may be interlocked. However, they are less attractive from an aesthetic standpoint.
A third category of paving stone overcomes to some degree the drawbacks of both first and second category paving stones. A third category paving stone is comprised of two or more sections having the shape of first category paving stones which are combined into one integral paving stone. An example, of such a paving stone is disclosed in U.S. Pat No. 4,128,357. The paving stone of that patent has a main section which is of a known octagonal shape, and a tail section which is of a known square shape, with the main and tail sections being formed as one paving stone. Another example of an interlocking paving stone, referred to as a trillium design, is shown in the brochure entitled, "Munich Two Interlocking Paving Stone" from Unilock, Ltd. of Georgetown, Ontario. The trillium design is comprised of three regular hexagonal shaped sections to form a cloverleaf pattern. Such integral paving stones can interlock for durability and stability. A disadvantage, however, is that they are susceptible of only a few different interlocking patterns, and the degree of interlock is limited.